Atmosphere tweel seal method and apparatus

ABSTRACT

Sealing the tweel relative to the opening through which it passes in the canal cover of an apparatus for producing float glass. A double-sectioned chamber surrounds the tweel whereby the outer section of the chamber serves as a liquid cooled support, and a gas is supplied to the inner section under pressure. The inner section has a porous wall facing the tweel through which the gas is forced to form a gaseous cushion or film preventing frictional contact between the porous wall and the tweel and minimizing the intrusion of atmospheric oxygen into the canal through the seal.

United States Patent Swillinger ATMOSPHERE TWEEL SEAL METHOD ANDAPPARATUS lnventor: Francis L. Swillinger, Perrysburg, OhioLibbey-Owens-Ford Company, Toledo, Ohio May 5, 1969 Assignee:

Int. Cl. ..C03b 18/02 Field of Search ..65/l 82 R, 99 A, 27, 32

References Cited UNITED STATES PATENTS Hideo Kita et al ..65/99 A 1 Jan.25, 1972 Primary Examiner-Arthur D. Kellogg Attorney-Collins and Oberlin57 ABSTRACT Sealing the tweel relative to the opening through which itpasses in the canal cover of an apparatus for producing float glass. Adouble-sectioned chamber surrounds the tweel whereby the outer sectionof the chamber serves as a liquid cooled support, and a gas is suppliedto the inner section under pressure. The inner section has a porous wallfacing the tweel through which the gas is forced to form a gaseouscushion or film preventing frictional contact between the porous walland the tweel and minimizing the intrusion of atmospheric oxygen intothe canal through the seal.

8 Claims, 6 Drawing Figures 5.9 I u 59 l PATENTED M25 M72 SHEET 2 OF 2Rm mm m vv IN LCd/nGQLOt J BACKGROUND OF THE INVENTION 1. Field of theInvention The present invention relates broadly to the manufacture offloat glass, and more particularly to an improved seal surrounding thetweel gate in the canal cover of a float glass producing apparatus in amanner to prevent abrasion due to physical contact between the cover andthe tweel gate and minimize intrusion of atmospheric oxygen into thecanal or escape of float bath atmosphere at the point of sealing.

2. Description of the Prior Art A conventional form of float glassforming apparatus is illustrated and described in U.S. Pat. No.3,083,551, granted Apr. 2, I963. As therein explained, the manufactureof flat glass by the float process involves delivering glass at acontrolled rate onto a bath of molten metal, such as tin, and advancingit along the surface of the bath under physical and thermal conditionswhich assure (I) that a floating body of molten glass which is free toflow laterally is established on the molten metal, (2) that from thismolten glass body there will develop on the surface of the metal bath abuoyant layer of molten glass of stable thickness, and (3) that thebuoyant body will be continuously advanced in ribbon form along thesurface of the molten metal bath and sufficiently cooled as it advancesto permit it to be removed unharmed from the bath by mechanicalconveying means.

As illustrated in FIGS. 6 and 7 and described in column 7, lines to 22of the patent, glass in molten form flows from the melting furnacethrough a canal, with such flow controlled by a regulating or controltweel and a tweel gate or blocking tweel as is common practice in thefloat glass art. It has heretofore been customary to construct both thetweels and the contact area where the tweels pass through the canalcover of refractory material.

With the prior art structures, realizing the necessity of frequentlyraising or lowering the control tweel to maintain flow control infeeding the molten glass onto the bath, the tweel was necessarily freeto move at the point where it passed through the canal cover. When thetolerance between the tweel and the canal cover was too close, the tweelphysically contacted the cover during movement and objectionableabrasion occurred, with the abraded material falling into the canal andcontaminating the molten glass. On the other hand, if the apparatus wereconstructed so that a wider gap existed between the tweel and the cover,whereby the abrasion was minimized, objectionable infiltration of oxygeninto the protective atmosphere of the bath chamber occurred. This oxygencombined with the hydrogen of the protective atmosphere to produce anextremely hot flame which caused a condition in the glass known asreboil, in which undesirable bubbles are formed in the glass. Regardlessof the exact prior art construction, these objectionable conditions werenot overcome simultaneously.

SUMMARY According to the present invention, the problem of the sealbetween the tweel and the roof of the canal is overcome, abrasionbetween adjacent refractory surfaces is eliminated, and the leakage ofoxygen into the canal is minimized, by the provision of an improvedgaseous seal located in the roof of the canal through which the tweelpasses. The seal surrounds the tweel with a cushioning film of gasescaping through a porous surface, preventing frictional contact andproviding a buffer of escaping gas to prevent the infiltration ofoutside oxygen.

It is, therefore, a primary object of the invention to provide animproved means of sealing the tweel in the opening of the canal cover ina manner that will avoid objectionable physical contact during movementof the tweel.

Another object is to provide such a sealing means which will permit thetweel to be freely raised and lowered while maintaining atmosphereintegrity within the canal by preventing infiltration of atmosphericoxygen through the seal.

Another object is to provide a sealing means which is selfsupporting andcompact and can be readily installed in the roof of the canal.

Other objects and advantages of the invention will become apparentduring the course of the following description when taken in connectionwith the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings, wherein like numeralsrefer to like parts throughout:

FIG. I is a longitudinal, vertical sectional view through arepresentative form of float glass apparatus embodying the invention;

FIG. 2 is a plan view of the apparatus of FIG. 1 with the superstructurepartially removed;

FIG. 3 is an enlarged plan view of the tweel and surrounding seal withportions cut away;

FIG. 4 is a transverse vertical section taken substantially along line4-4 of FIG. 3;

FIG. 5 is an enlarged perspective view of the seal with parts brokenaway; and

FIG. 6 is an enlarged transverse view of the seal taken substantiallyalong line 6-6 of FIG. 5 and showing the relationship of the porous wallto the adjacent tweel.

DESCRIPTION OF THE INVENTION Referring to the drawings, there isillustrated generally in FIGS. 1 and 2 a typical float glass machinesimilar to the one disclosed in the aforementioned US. Pat. No.3,083,551. Shown at 10 is the forehearth of a continuous glass meltingfurnace, from which a supply of molten glass 11 is delivered through andover a spout assembly 12 in an amount regulated by a control tweel 13. Aso-called blocking tweel I4 is positioned upstream from the controltweel 13 so that it can be lowered to shut off the flow of molten glassalong the forehearth or canal I0 to the control tweel should it bedesired to do so.

The glass flows from the spout 12 onto a relatively wide metal bath 15contained in a tank 16, and forms a buoyant body of molten glass,indicated at 17, from which a buoyant layer 18 of stable thicknessdevelops in ribbon form.

The metal bath 15 in the tank 16 and the headspace 19 over the bath areheated by radiant heat directed downwardly from heaters 20. Theheadspace is enclosed by sidewalls 21 containing windows 22, and endwall 23 at the inlet end of the tank, an end wall 24 at the outlet endof the tank, and a roof structure 25. The enclosed headspace volume 19,usually referred to as a plenum chamber, along with an extension 26 overthe spout area, contains enough space to maintain a sufficient amount ofprotective gas, known as the float or bath atmosphere, over that part ofthe metal bath 15 that is exposed at each side of the buoyant body 17and layer 18 of glass. The protective gas is one which will not reactchemically with the metal bath 15 to produce contaminants of the glassor the bath itself. For example, the gas may be a mixture of nitrogenand hydrogen. By maintaining slightly positive pressure within theheadspace l9, entrance of atmospheric air is theoretically prevented andthe integrity of the protective gas is maintained. However, as apractical matter, it has been found that this is not always true at allpoints in the system. The float atmosphere is supplied in sufficientquantity to the headspace 19 through a duct system which includes a mainheader 27 with branches 28 and chamber inlet ducts 29.

The temperature within the tank 16 is controlled by the radiant heaters20 such that the buoyant layer or ribbon 18 is progressively cooled asit moves over the molten metal bath to the discharge end thereof, bywhich time the ultimate ribbon 30 reaches a condition of stiffnessadequate to allow it to be transferred to an adjacent annealing Iehr bymechanical con-' veying means without detriment to its lower surface.

One type of mechanical conveying means that may suitably be employed forthis purpose includes supporting rollers 31, 32 and 33 and superimposedroller 34 mounted outside of the discharge throat of the tank. Any orall of the rollers may be driven by known means and cooperate to apply atractive effort to the ribbon of glass moving towards the outlet endsufficient to advance it along the bath. An ultimate ribbon 30 of athickness less than the equilibrium thickness of the buoyant layer 18may be obtained by increasing the speed of the rollers 31 to 34 andthereby increasing their tractional effort and attenuating the moltenglass body 18 of stable thickness.

The molten glass 11 flows along the forehearth or canal between oppositesidewalls 35. A roof 36 over the canal and an associated roof 37 overthe extension 26 of the spout area enclose the canal and spout area toprevent adverse cooling effects of air currents upon, and entry offoreign matter into, the molten glass flowing through the canal into thebath. The control tweel 13 and blocking tweel 14 extend through thecanal roof 36 and/or roof extension 37, and are supported from above asby conventional devices (not shown) which engage dovetailed sections 38extending along their top edge.

It will be appreciated that the amount of glass delivered over the spoutlip 12 onto the bath is regulated by the control tweel 13. it isconsequently necessary that the tweel 13 be freely verticallyadjustable, and thus it must be free to move at the point where itpasses through the roof 36 and/or roof extension 37. Contamination ofthe molten glass in the canal at this point by abraded particlesresulting from physical contact between the refractory tweel and canalroof is highly undesirable, as is the aforementioned reboil conditiondue to infiltration of air from outside the canal chamber.

As previously explained, reduction of one of the undesirable effectsheretofore has tended to cause an increase in the other, i.e.,decreasing the tolerance or space between the tweel and roof to reducethe amount of air infiltration resulted in greater abrasive contactbetween the adjacent surfaces, while increasing the tolerance reducedabrasive contact but increased the amount of air infiltration.

in accordance with the present invention these problems are overcome byprovision of a novel seal employing a gaseous cushion or film compatiblewith the bath atmosphere adjacent the surface of the tweel. The filmprevents frictional contact between the moving surfaces even though thespace therebetween may be very small, and also provides a buffer of gascompatible with the atmosphere of the bath which prevents infiltrationof outside air.

The sealing device, shown generally at 39, surrounds the tweel and, forease of fabrication and installation, may be made in two generallyL-shaped complementary sections 40 and 41 (FIG. 3). The L-shapedsections may be supported by resting upon ledges 42,and 43 at the edgeof the members forming the roof 36 or 37, respectively, or by otherconventional support means. Of course, it is contemplated that thedevice 39 might also be fabricated as a single unit encircling thetweel.

Each of the sections 40 and 41 is comprised of a tubular cooling andsupport member 44 to which is secured a pressure duct 45. A conduit 46extends axially within the tubular member 44. At one of its ends theconduit 46 is connected through a coupling 47 to a source of heatabsorbing medium, and at its other end, adjacent the closed end of thetubular member 44, it discharges the fluid into the chamber 48 betweenthe tubular member and conduit. A second coupling 49 is provided at theend of the tubular member 44 for connecting the chamber 48 to a suitableeffluent line. Thus, the heat absorbing medium enters the conduit 46through the coupling 47, flows to the opposite end where it isdischarged into the chamber 48 and flows back to the entry point fordischarge through the coupling 49 in a counterflow manner.

The pressure duct 45 is formed by spaced walls 50 extending from thetubular member 44, and a porous wall 51 which faces the adjacent surfaceof the tweel 13. A manifold pipe 52 having spaced perforations 53therein is locatedwithin the duct 45 and connected, through a nipple 54at one end, to a source of suitable gas under pressure. The ends of thepressure duct 45, as well as the tubular member 44, are closed as byplates 55. There is thus formed a plenum chamber 56 within the pressureduct 45. As gas is supplied to the manifold pipe 52 under pressure, itemerges from the spaced perforations 53 to create a uniform pressurewithin the plenum chamber 56 throughout its length. The gas is forcedthrough the porous wall 51 facing the tweel 13 to form a thin film 57 ofgas therebetween (FIG. 6).

Suitable piping, shown generally at 58, may be arranged in any preferredmanner to connect the couplings 47 of the sections 40 and 41 to a sourceof heat absorbing medium, generally water, and similar piping S9 isarranged to connect the couplings 49 to a disposal means for the spentmedium. Piping 60 connects the manifold pipes 52 to a supply of gasunder pressure through the nipples 54.

The wall 51 may advantageously be formed of any material which willwithstand the temperatures encountered while permitting passage of thegas to form the film 57. Porous metal has been found particularlysuitable for this purpose; and Feltmetal, a product commerciallyavailable from the Huyck Equipment Company, Melford, Conn., has beenemployed with excellent results. Sintered and perforated metallicmembers are examples of other materials which may be employed.

The gas supplied to the plenum chamber 56 must, of course, be compatiblewith the bath atmosphere since some of it may enter the enclosed areaover the canal and mingle with the bath atmosphere in the headspace 19.A mixture of gases equivalent to the bath atmosphere itself may beemployed. Excellent results have been obtained using pure nitrogen forthis purpose. The volume of gas required is relatively small, and thepressure at which it is supplied will depend upon the porosity of thewall 51. However, it has been found that with a wall 51 of theabove-mentioned Feltmetal, supplying nitrogen at a pressure in theapproximate range from about 10 to I00 p.s.i., will create afilm 57providing a suitable seal around the tweel. A pressure of about 56p.s.i. has been found to give excellent results while using only about500 cubic feet (STP) of nitrogen per hour. of course, part of thisnitrogen finds its way into the bathatmosphere so that not all of it iswasted.

The gas film S7, in addition to preventing infiltration of externalatmosphere around the tweel, prevents the wall 51 from coming intodirect contact with the tweel even though the gap therebetween may be.very small. Thus, the gap can be minimized, and yet the lubricatingeffect of the film 57 prevents abrasive removal of particles from thetweel.

The blocking tweel 14, while it is held up out of the glass and notvertically adjusted during normal operations, must be adapted to belowered at any time on short notice to discontinue flow of molten glassto the spout and bath. For this reason, it will be readily appreciatedthat while for purposes of simplification the seal has been illustratedonly in connection with the control tweel 13, it may also advantageouslybe employed with the blocking tweel 14. I

It is to be understood that the form of the invention herewith shown anddescribed is to be taken as an illustrative embodiment only of the same,and that various changes in the shape, size and arrangement of parts, aswell as various procedural changes may be resorted to without departingfrom the spirit of the invention.

I claim 1. ln a seal for a movable tweel member extending through thecover over the canal through which molten glass flows from a meltingfurnace to a float glass apparatus, the improvement comprising a porousmember incorporated in said cover facing at least the major surfaces ofand closely adjacent said tweel member at the point where it passesthrough said cover, and means supplying and forcing a gas through saidporous member to forma gaseous film on said porous member filling thegap between said porous member and said tweel member and preventingabrasive contact with said tweel during movement thereof. 3

2. A seal for a movable tweel member as claimed in claim 1, including aduct in said duct under pressure whereby said gas is forced through saidporous wall to form said gaseous film.

5. A seal for a movable tweel member as claimed in claim 4, wherein saidtubular cooling and support member comprises said outer tubular member,and returns to said discharge connection effecting a counterflow system.

6. A seal for a movable tweel member as claimed in claim 4,

wherein sald pressure duct 7. A sea] for a movable tweel member asclaimed in claim 6, including a manifold pipe mounted within saidrectangular ing abrasive contact between said tweel and cover.

P0405 UNITED STATES PATENT OFFIQE CERTIFECATE OF CORRECTIQN Patent 3,637,363 Dated January 25 1972 Inventor(s) Francis L. swilling er It iscertified that error appears in the above-identified patentand that saidLetters Patent are hereby corrected as shown below:

Col. 5 lines 21 and 22 cancel "said inlet end of said .1

outer tubular member', means connection at" Signed and sealed this 22ndday of August l972.

(SEAL) Attest: I

EDWARD I'-i.FLETCHER,JR. ROBERT GOTTSGHALK Attesting OfficerCommissioner of Patents

1. In a seal for a movable tweel member extending through the cover overthe canal through which molten glass flows from a melting furnace to afloat glass apparatus, the improvement comprising a porous memberincorporated in said cover facing at least the major surfaces of andclosely adjacent said tweel member at the point where it passes throughsaid cover, and means supplying and forcing a gas through said porousmember to form a gaseous film on said porous member filling the gapbetween said porous member and said tweel member and preventing abrasivecontact with said tweel during movement thereof.
 2. A seal for a movabletweel member as claimed in claim 1, including a duct in said coversubstantially surrounding said tweel, said porous member comprising awall of said duct, and means supplying said gas to said duct.
 3. A sealfor a vertically movable tweel member as claimed in claim 2, whereinsaid duct is comprised of two complementary ''''L''''-shaped sections.4. A seal for a movable tweel member as claimed in claim 1, including atubular cooling and support member substantially surrounding said tweel,means for circulating a heat absorbing medium through said tubularmember, a pressure duct secured to said tubular member and substantiallysurrounding said tweel, said porous member comprising the wall of saidduct facing said tweel, and means supplying said gas to said duct underpressure whereby said gas is forced through said porous wall to formsaid gaseous film.
 5. A seal for a movable tweel member as claimed inclaim 4, wherein said tubular cooling and support member comprises anouter tubular member having ends closed by plates, an inner conduitmounted axially within said outer tubular member and extending from aninlet connection at said inlet end of said outer tubular member, meansconnection at one end of said outer tubular member to a point adjacentto the other end thereof, a discharge connection at said inlet end ofsaid outer tubular member, means connected to said inlet connection forsupplying a heat absorbing medium to said inner conduit, and meansconnected to said discharge connection for disposing of spent heatabsorbing medium, whereby said heat absorbing medium enters at one endof said tubular member, flows the length of said inner conduit, isemitted into said outer tubular member, and returns to said dischargeconnection effecting a counterflow system.
 6. A seal for a movable tweelmember as claimed in claim 4, wherein said pressure duct comprises achamber rectangular in cross section and having said porous wall, a pairof spaced walls extending from said porous wall and secured to saidouter tubular member, said outer tubular member forming the fourth wallof said chamber, and a plate closing each end of said chamber.
 7. A sealfor a movable tweel member as claimed in claim 6, including a manifoldpipe mounted within said rectangular duct and extending axially from aninlet connection at one end of said duct to a closed termination at theother end thereof, said pipe having a plurality of perforations spacedthroughout its length to distribute said gas uniformly in said chamber.8. In a method of adjusting the elevation of a tweel extending throughan opening in the cover over the cAnal through which molten glass flowsfrom a melting furnace to a float glass bath, the improvement comprisingsupplying a gas compatible with the atmosphere within said canal throughthe walls defining said opening and facing at least the major surfacesof said tweel under sufficient pressure to maintain a film of said gaswithin the gap between the tweel and cover, said gas filling said gapand flowing outwardly therefrom to prevent movement of atmospherethrough said gap from either side of said cover to the other, and movingsaid tweel through said opening to the desired elevation with said filmof gas preventing abrasive contact between said tweel and cover.